A critical step in realizing molecular scale electronics is the elucidation of molecular properties that are analogous to those found in conventional electronic components. In particular, nonlinear current-voltage behaviors are of interest as these behaviors form the basis of several critical classes of devices including switches, amplifiers, and frequency converters. See Sze, S. M., Physics of Semiconductor Devices; 2nd ed.; John Wiley and Sons: New York, N.Y., United States of America, 1981; pp 513-520.
In two terminal devices, the nonlinear current-voltage behavior termed negative differential resistance (NDR) is a key property of the Esaki diode and resonant tunneling diodes (RTDs). NDR has also been observed in molecule-based systems. Mathews. R. H., et al., Proc. IEEE 1999, 87, 596-605; Chen, J., et al., Science 1999, 286; Xue, Y. et al., Phys. Rev. B 1999, 59, R7852-7855; Gaudioso, J., et al., Phys. Rev. Lett. 2000, 85, 1918-1921; Chen, J., et al., Appl. Phys. Lett. 2000, 77, 1224-1226. NDR behavior in RTDs can be tuned with the materials used, dopant concentration, and the physical structure of the device. Zeng, C., et al., Appl. Phys. Lett. 2000, 77, 3595-3597; Kinne, M. and Barteau, M. A. Surf. Sci. 2000, 447, 105-111; Sun, J. P., et al., Proceedings of the IEEE 1998, 86, 641-661; Zhao, P., et al., J. Appl. Phys. 2000, 87, 1337-1349; Seabaugh, A.; Hu, Z.; Liu, Q.; Rink, D.; Wang, J. “Silicon-Based Tunnel Diodes and Integrated Circuits” In 4th International Workshop on Quantum Functional Devices; Research and Development Association for Future Electron Devices: Japan, 2000, pp 5-8.; Huang, C. Y., et al., Elect. Lett. 1994, 30, 1012-1013; Zhao, P., et al., IEEE Trans. Elect Dev. 2001, 48, 614-627; Schulman. J. N., et al., IEEE Elect. Dev. Lett. 1996, 17, 220-222. In contrast, control of the parameters governing NDR behavior in molecular systems is just beginning to be explored. See e.g., Karzazi. Y., et al., J. Am. Chem. Soc. 2001; Xue, Y., et al., J. Chem. Phys. 2001, 115, 4292-4299. Additionally, although there have been several reports examining the relationship between NDR and electroactivity in organic (Tao. N. J., Phys. Rev. Lett. 1996, 76, 4066-4069) and inorganic systems (Kinne, M. and Barteau, M. A. Surf Sci. 2000, 447, 105-111; Kaba, M. S., et al., J. Vac. Sci. Technol. A 1997, 15, 1299-1304), the general phenomenon of NDR in molecular scale systems is not well understood. Indeed, there is currently no known sound mechanistic basis as to how NDR is generated in molecular systems. The present invention addresses this and other needs in the art.